Conventionally, in an exposure apparatus using pulsed light, a light emission instruction (trigger) is given from the exposure apparatus side to the light source and the light source generates a corresponding exposure light. That is to say, exposure operations are performed by the exposure apparatus side to output a trigger signal to the light source so that it coincides with the timing of the apparatus stage drive. By doing this, uniformity of exposure quantity can be obtained within the exposure field.
On the other hand, one kind of EUV light source uses the X-rays (EUV light) radiating from plasma produced from a target material which is supplied intermittently. As this type of light source, there is for example a droplet laser produced plasma X-ray source, which produces plasma by impinging laser light to the droplet target discharged from the tip of a nozzle. See Japanese Patent Application Publication No. 2000-215998 Official gazette.
However, in this type of light source, the moment at which EUV light is generated is dependent on the timing of supply of the target material, and is not related to timing used in the exposure apparatus. For this reason, even if the exposure apparatus outputs a trigger signal to the light source, the exposure apparatus does not generate light at the desired timing. This timing slip (delay) is at most the reciprocal of the repetition frequency of the light source. For example, if the repetition frequency is 1 kHz, the maximum delay is 1 ms.
For this reason, in the worst case, the number of pulses radiated at the scan starting point and scan end point within the exposure field is deficient by 1 pulse due to the delay between the start timing of movement of the exposure apparatus stage and the timing of EUV light generation, and uniformity of exposure within the field ends up deteriorating.